中文摘要：

从理论上提出了硅的一种新型金属性亚稳相,并通过弹性常数和声子谱的计算验证了该结构在常压下的稳定性.该结构可以通过以？-La Si5为前驱物,将其中的La原子去除获得.该结构中隧道型空隙的存在使其密度低于金刚石型结构的Si-I相.在这种结构中,有40%的硅原子为5配位,其他硅原子为4配位.电子结构的计算表明该结构具有金属导电性.导电性主要由于5配位原子的存在导致价电子出现离域性.配位数的改变也使得硅原子之间发生了一定的电荷转移,出现离子性.该结构的化学键中同时存在共价性、金属性和离子性.

英文摘要：

Silicon plays an important role in the mordern photovoltaic and semiconductive industry. In addition, it also arouses great interest in the scientific research due to its structural variety. In experiment, more than thirteen silicon allotropes have been prepared through high pressure or chemical method. Meanwhile, various new silicon structures have been proposed theoretically. The structural variety leads to various electronic properties, including semiconductivity with different band gaps, metallicity, and superconductivity. These electronic properties have a close relationship with the silicon atomic coordination. For example, silicon allotropes with merely four coordinated atoms usually exhibit semiconductive property, while silicon structures with higher coordination number would show metallicity or superconductivity. Thus far, all the synthesized metastable silicon allotropes are composed of four coordinated atoms. Silicon allotropes with higher coordination numbers are mainly high pressure phases which could not be quenched to the ambient condition. One might wonder whether there would be possibility for the preparation of metastable metallic silicon structures. In this paper, a new metallic metastable silicon allotrope has been proposed theoretically using the particle swarm optimization method. This structure was also found when removing the La atoms in ？-La Si5. Its stability was verified by calculating its elastic constants and phonon spectrum. It might be achieved by removing the La atoms from the ？-La Si5 precursor, which is analogous with the recent preparation of Si24. The tunnel-like voids in this structure lead to its lower density than that of the Si-I phase. There are 40% five coordinated silicon atoms, wheras the others are four coordinated. Since silicon has four valence electrons, sp3 hybridized four connected silicon just satisfy the octet rule and would show semiconductivity. The change of coordination number results in a charge transfer between different atoms as indicated by the atom